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24 #include "compiler/nir/nir_builder.h"
28 * Implements the WaPreventHSTessLevelsInterference workaround (for Gen7-8).
30 * From the Broadwell PRM, Volume 7 (3D-Media-GPGPU), Page 494 (below the
31 * definition of the patch header layouts):
33 * "HW Bug: The Tessellation stage will incorrectly add domain points
34 * along patch edges under the following conditions, which may result
35 * in conformance failures and/or cracking artifacts:
38 * * INTEGER partitioning
39 * * All three TessFactors in a given U or V direction (e.g., V
40 * direction: UEQ0, InsideV, UEQ1) are all exactly 1.0
41 * * All three TessFactors in the other direction are > 1.0 and all
42 * round up to the same integer value (e.g, U direction:
43 * VEQ0 = 3.1, InsideU = 3.7, VEQ1 = 3.4)
45 * The suggested workaround (to be implemented as part of the postamble
46 * to the HS shader in the HS kernel) is:
53 * (TF[INSIDE_U] > 1.0) ||
54 * (TF[INSIDE_V] > 1.0) )
56 * TF[INSIDE_U] = (TF[INSIDE_U] == 1.0) ? 2.0 : TF[INSIDE_U];
57 * TF[INSIDE_V] = (TF[INSIDE_V] == 1.0) ? 2.0 : TF[INSIDE_V];
60 * There's a subtlety here. Intel internal HSD-ES bug 1208668495 notes
61 * that the above workaround fails to fix certain GL/ES CTS tests which
62 * have inside tessellation factors of -1.0. This can be explained by
63 * a quote from the ARB_tessellation_shader specification:
65 * "If "equal_spacing" is used, the floating-point tessellation level is
66 * first clamped to the range [1,<max>], where <max> is implementation-
67 * dependent maximum tessellation level (MAX_TESS_GEN_LEVEL)."
69 * In other words, the actual inner tessellation factor used is
70 * clamp(TF[INSIDE_*], 1.0, 64.0). So we want to compare the clamped
71 * value against 1.0. To accomplish this, we change the comparison from
72 * (TF[INSIDE_*] == 1.0) to (TF[INSIDE_*] <= 1.0).
75 static inline nir_ssa_def
*
76 load_output(nir_builder
*b
, int num_components
, int offset
, int component
)
78 nir_intrinsic_instr
*load
=
79 nir_intrinsic_instr_create(b
->shader
, nir_intrinsic_load_output
);
80 nir_ssa_dest_init(&load
->instr
, &load
->dest
, num_components
, 32, NULL
);
81 load
->num_components
= num_components
;
82 load
->src
[0] = nir_src_for_ssa(nir_imm_int(b
, 0));
83 nir_intrinsic_set_base(load
, offset
);
84 nir_intrinsic_set_component(load
, component
);
86 nir_builder_instr_insert(b
, &load
->instr
);
88 return &load
->dest
.ssa
;
92 emit_quads_workaround(nir_builder
*b
, nir_block
*block
)
94 b
->cursor
= nir_after_block_before_jump(block
);
96 nir_ssa_def
*inner
= load_output(b
, 2, 0, 2);
97 nir_ssa_def
*outer
= load_output(b
, 4, 1, 0);
99 nir_ssa_def
*any_greater_than_1
=
100 nir_ior(b
, nir_bany(b
, nir_flt(b
, nir_imm_float(b
, 1.0f
), outer
)),
101 nir_bany(b
, nir_flt(b
, nir_imm_float(b
, 1.0f
), inner
)));
103 nir_if
*if_stmt
= nir_if_create(b
->shader
);
104 if_stmt
->condition
= nir_src_for_ssa(any_greater_than_1
);
105 nir_builder_cf_insert(b
, &if_stmt
->cf_node
);
107 /* Fill out the new then-block */
108 b
->cursor
= nir_after_cf_list(&if_stmt
->then_list
);
110 inner
= nir_bcsel(b
, nir_fge(b
, nir_imm_float(b
, 1.0f
), inner
),
111 nir_imm_float(b
, 2.0f
), inner
);
113 nir_intrinsic_instr
*store
=
114 nir_intrinsic_instr_create(b
->shader
, nir_intrinsic_store_output
);
115 store
->num_components
= 2;
116 nir_intrinsic_set_write_mask(store
, WRITEMASK_XY
);
117 nir_intrinsic_set_component(store
, 2);
118 store
->src
[0] = nir_src_for_ssa(inner
);
119 store
->src
[1] = nir_src_for_ssa(nir_imm_int(b
, 0));
120 nir_builder_instr_insert(b
, &store
->instr
);
124 brw_nir_apply_tcs_quads_workaround(nir_shader
*nir
)
126 assert(nir
->info
.stage
== MESA_SHADER_TESS_CTRL
);
128 nir_function_impl
*impl
= nir_shader_get_entrypoint(nir
);
131 nir_builder_init(&b
, impl
);
133 /* emit_quads_workaround() inserts an if statement into each block,
134 * which splits it in two. This changes the set of predecessors of
135 * the end block. We want to process the original set, so to be safe,
136 * save it off to an array first.
138 const unsigned num_end_preds
= impl
->end_block
->predecessors
->entries
;
139 nir_block
*end_preds
[num_end_preds
];
142 set_foreach(impl
->end_block
->predecessors
, entry
) {
143 end_preds
[i
++] = (nir_block
*) entry
->key
;
146 for (i
= 0; i
< num_end_preds
; i
++) {
147 emit_quads_workaround(&b
, end_preds
[i
]);
150 nir_metadata_preserve(impl
, 0);